The present invention relates to a vehicle height adjustment system for an automotive vehicle, and more specifically relates to a vehicle height adjustment system of the suspension height adjustment type which is particularly adapted for preventing imbalances between the suspension loadings imposed on the various vehicle wheels.
The present invention has been described in Japanese Patent Application Ser. No. 60-235652 (1985), filed by applicants the same as the applicants or those assigned or owed duty of assignment of the present patent application; and the present patent application hereby incorporates into itself by reference the text of said Japaneses Patent Application and the claims and the drawings thereof; a copy is appended to the present application.
Further, the present inventors wish hereby to attract the attention of the examining authorities to copending Patent Applications Ser. Nos. 921,138 filed Oct. 21, 1986, 921,251 filed Oct. 21, 1986, 921,451 filed Oct. 22, 1986 and 921,468, filed Oct. 22, 1986, which may be considered to be material to the examination of the present patent application.
The following problem can arise in the case where a vehicle is fitted with a vehicle height adjustment system comprising: a plurality of actuators which are provided for resiliently suspending the vehicle wheels from its body and which are adapted to increase or decrease vehicle height at locations corresponding to the associated vehicle wheels as respective results of supplying or discharging working fluid to or from variable volume working fluid pressure chambers of said actuators; a plurality of working fluid supplying and discharging means which are provided corresponding to the actuators and which serve to supply or discharge the working fluid to or from said pressure chambers of said actuators (such working fluid supplying and discharging means are typically controlled by duty ratio control); a vehicle height detecting means for sensing vehicle body heights over the various wheels thereof (the terms "wheel height" and "suspension height" will be utilized hereinafter in this specification, although strictly speaking it is the suspended heights of the portion of the vehicle body over each of its wheels as set by the vehicle suspension which are meant); and a control means for controlling the various working fluid supplying and discharging means based upon the data sensed by the vehicle height detecting means in order to control the adjustment of the suspension heights of the vehicle wheels to certain determinate wheel heights, as proposed, for example, in the specifications of Japanese Patent Laying Open Publication Serial No. Sho 60-85005 (1985) and Japanese Patent Laying Open Publication Serial No. Sho 60-235654 (1985), both of which were filed by an applicant the same as one of the applicants or one of the assignees or one of the entitles owed duty of assignment of the present application and which it is not intended hereby to admit as prior art to the present patent application except to the extent in any case required by applicable law. Namely, in such a case, the hydraulic fluid supply and draining means for the actuators are controlled by the control device according to a feedback process, based upon the deviations between the actual wheel heights and certain determinate target wheel heights (or "standard" wheel heights), as a result of which the suspension height of the whole vehicle, taken overall, can indeed be satisfactorily adjusted, but the balance between the loadings imposed upon each vehicle wheel, in other words the proportions in which the supporting of the weight of the vehicle is split up between the various vehicle wheels, can be easily disturbed, and therefore it could in the worst case occur that one of the vehicle wheels comes to be in a floating or semi floating state with relatively little suspension pushing force biasing said vehicle wheel downwards against the road surface, and this can deteriorate a vehicle stability and cause excessive and/or uneven tire wear, among other problems.
Further, in general, in the operational conditions where a vehicle such as an automobile is turning as for example around a curve, the body of the vehicle experiences rolling, i.e. the vehicle body inclines in the radially outward direction and tips towards the wheels on its radially outward edge, and this body rolling can easily result in deterioration of the drivability of the vehicle.
In order to cope with the above problems, it might be considered, during such a turn, to increase the damping effect of those of the shock absorber means which are fitted to said vehicle wheels on the radially outward edge of the vehicle, and/or to increase the spring constant of those of the spring means which are fitted to said vehicle wheels on the radially outward edge of the vehicle. Such a concept is outlined in Japanese Patent Laying Open Publication Serial No. 59-120509 (1984) and in Japanese Patent Application Serial No. Sho 59-172416 (1984), neither of which is it intended hereby to admit as prior art to the present patent application except to the extent in any case required by applicable law; and reference should also be made to Japanese Utility Model Laying Open Publication Serial No. 59-35105 (1984), Japanese Patent Laying Open Publication Serial No. 53-26021 (1978), Japanese Patent Laying Open Publication Serial No. 58-167210 (1983), and Japanese Utility Model Laying Open Publication Serial No. 56-147107 (1981), again none of which is it intended hereby to admit as prior art to the present patent application except to the extent in any case required by applicable law. However, with these concepts, merely the suspension of the vehicle on the outer side edge thereof with respect to the turn is hardened, and thus the rolling of the vehicle body may be somewhat attenuated as compared with the case when such suspension hardening is not performed, but the rolling of the vehicle body cannot necessarily be adequately prevented. Accordingly, such a concept does not really resolve the problem.